A new psychophysiological assessment strategy will be evaluated with human neonates. The research will test the hypothesis that individual differences in neonatal cardiac vagal tone can prospectively identify infants at greatest risk for developmental disabilities. The research will employ a non-invasive measure of vagal tone derived from the rhythmic heart rate pattern. The specific objective of the proposed research is to identify, through non-invasive monitoring of vagal tone, neonates who will have a high probability of manifesting developmental problems (e.g., deficits in cognitive, social, sleep, motor, and health processes). The techniques tested in the proposed research have the potential to evolve into a neonatal assessment instrument capable of predicting developmental outcome.